1. Field of the Invention
The present invention relates to a compressed picture information recording apparatus for recording compressed picture information on a recording disk.
2. Description of the Related Art
FIG. 1 shows the structure of a recording apparatus for subjecting a video signal, reproduced by a VTR (Video Tape Recorder), to image compression and then recording the compressed video signal on a recording disk.
In FIG. 1, digital video signals reproduced by a VTR 1 are supplied to an image compression encoder 2. The image compression encoder 2 performs compression coding on such digital video signals, yielding compressed video signals, and converts the compressed video signals to have the proper recording format. The image compression encoder 2 then supplies the resultant video signals to an LBR (Laser Beam Recorder) 3. The LBR 3 sequentially records the format-changed compressed video signals on the recording disk.
The data recording rate, R0, of such a recording disk is constant. Therefore, the image compression encoder 2 carries out the compression coding on the minimum condition that the producing rate, R1, of the compressed video signals obtained in the compression coding does not exceed the recording rate R0 and in such a way that the producing rate R1 sufficiently approaches the recording rate R0.
At this time, the producing rate of compressed video signals, which are obtained based on video signals with a relatively complex image quality in the image compression encoder 2, is greater than the producing rate of compressed video signals, which are obtained based on video signals with a simple image quality. Consequently, the producing rate R1 generally varies in the range of several tens to 100% with respect to the recording rate R0.
The image compression encoder 2 is demanded to perform effectively compressing data with as small variation of the producing rate R1 as possible, and to affix invalid data to the produced data as shown in FIG. 2 with respect to the producing rate that varies at last, establishing the following condition.
Producing rate R1+Invalid rate R2=Recording rate R0
As a result, the variable producing rate is forcibly set to a constant rate (equivalent to the recording rate R0) so that both rates match with each other.
GOP (Group of Pictures) in FIG. 2 is a processing unit in the compression coding of video signals as specified by the ISO 11172 MPEG (Motion Picture Coding Experts Group) system.
With the use of a recording disk whose recording rate R0 is constant, even when the producing rate of the compressed video signals obtained by the image compression encoder is relatively small, data irrelevant to the picture to be recorded is also recorded at the time of recording. The recording efficiency is therefore deteriorated.